Indirectly heated cathode



June 12, 1956 K. J. GERMESHAUSEN INDIRECTLY HEATED CATHODE Original Filed May I5,

FIG.2

INVENTOR KENNETH J. GERMESHAUSEN ATTO NEYS INDIRECTLY HEATED CATHDEE Kenneth J. Germeshausen, Newton Center, Mass, as-

signor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Original application May 3, 1946, Serial No. 666,880, now Patent No. 2,678,403, dated May 11, 1954. Di= vided and this application April 16, 1952, Serial No. 282,619

1 Claim. (Cl. 313-=-337) This invention relates in general to hydrogen thyratrons and more particularly to the prevention of grid emission in hydrogen thyratrons of the inside coated cathode type.

This application is a division of copending application, Serial No. 666,880, filed May 3, 1946, now Patent No. 2,678,403, entitled Grid Probe Structure.

Thyratron tubes have many applications in electronic circuits. Hydrogen thyratrons have been developed having advantages over other thyratrons which make them more desirable in many applications. A hydrogen thyratron is disclosed in patent application entitled Hydrogen Thyratron, Serial No. 576,113, filed February 3, 1945, by Kenneth J. Germeshausen, now Patent No. 2,518,879. Grid emission, caused by cathode coating materials being evaporated from the cathode and deposited on the grid has proved troublesome in these tubes.

It is therefore an object of this invention to prevent grid emission in hydrogen thyratron tubes employing inside coated cathodes.

It is a further object of this invention to provide a tube structure which maintains good grid starting characteristics while preventing such grid emission.

These and other objects will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 illustrates the structure of this invention; and

Fig. 2 shows an improved type heater for oxide cathodes of the type used in some thyratron tubes.

The invention will now be described in detail with reference to Fig. 1, which shows the electrode structure of a hydrogen filled thyratron type tube. For simplicity the envelope 11 has been symbolically shown. An oxide film 10 is coated on the inside surface and enclosed by a cylindrical conductive structure 12 which has an aperture 14 at the top as shown. The electron discharge from oxide film 10 passes through this orifice toward the grid and anode. A cylindrical grid structure 16 is placed around cylindrical structure 12. This grid has a transverse mesh 18 between the top of cylindrical structure 12 and anode 20.

To prevent grid emission, it is necessary to keep evaporated metal, such as barium, from the oxide film 10 away from mesh section 18 of the grid structure. This is ac complished by placing a baifie 22 between the cathode structure 12 and grid mesh 18. This battle is conductively attached to the cathode structure 12 by a supporting member 24. The baflle when connected in such manner shields the grid 18 and prevents substantially all evaporated metal from reaching the grid mesh 18. Battle Fnited dtates Patent Patented June 12, 1956 22 connected in this manner shields the cathode so completely that it is diflicult to start a discharge between grid and cathode to start thyratron conduction. To eliminate this difliculty and increase control sensitivity a small diameter probe 26 is attached to grid mesh 18 and cxtends axially through a small aperture in the center of bafile 22 a short distance in the direction of cathode structure 12. This probe 26 enables the start of a discharge between grid mesh 18 and cathode 12, which readily reaches the anode. The small area of the probe 26 exposed to the cathode discharge, its location, and small cross-section prevent it from causing grid emission difficulties even though some evaporated metal may be deposited on the end of the probe.

Thus it may be seen that this invention provides means for preventing grid emission trouble in hydrogen thyratrons of inside coated cathode types without interfering with the desirable operating features of such tubes.

Now referring to Fig. 2 there is shown an improved type heater for use with oxide cathodes. A cathode 40 with an electron emissive coating 42 is heated by a heater element 44 inside the cathode sleeve 40. The heater element 44 is constructed of a ribbon shaped metal such as tungsten. The cross-section of the ribbon is selected such that adjacent turns of the helically Wound ribbon touch each other and completely fill the space inside the cathode sleeve 40. As the heater 44 is operated at low voltage, no special insulation is required. This construction prevents sagging of the heater, and it is thus possible to use ribbon of less refractory metal than tungsten, as for example, molybdenum. In addition to these features, the arrangement shown, wherein adjacent turns are in contact presents almost a uniform heating surface to provide very uniform heating of the cathode sleeve 49 and coating 42.

It is believed that the construction and operation as well as the advantages of my'improved thyratron tube structure will be apparent from the foregoing detailed description thereof. It will also be apparent that while 1 have shown and described my invention, in a preferred form, changes may be made in the apparatus disclosed without departing from the spirit of the invention as sought to be defined in the following claim.

What is claimed is:

In an electron tube the combination of a cylindrical cathode sleeve having an electron emissive outer coating, a low voltage heater element within said sleeve and in close contact therewith, said heater element consisting of a metal ribbon helically wound with adjacent turns thereof in contact to form a substantially cylindrical heated cathode area.

References Cited in the file of this patent UNITED STATES PATENTS 1,722,468 Hunter July 30, 1929 1,852,023 Parker Apr. 5, 1932 1,992,550 Spencer Feb. 26, 1935 2,002,667 Knoll May 28, 1935 2,078,360 Ziegenbein Apr. 27, 1937 2,083,346 Ronci June 8, 1937 2,478,841 Schmidt Aug. 9, 1949 

